An investigation on possible effect of leaching fractions physiological responses of hot pepper plants to irrigation water salinity.

BACKGROUND: The modification effect of leaching fraction (LF) on the physiological responses of plants to irrigation water salinity (ECiw) remains unknown. Here, leaf gas exchange, photosynthetic light-response and CO2-response curves, and total carbon (C) and nitrogen (N) accumulation in hot pepper leaves were investigated under three ECiw levels (0.9, 4.7 and 7.0 dS m- 1) and two LFs treatments (0.17 and 0.29). RESULTS: Leaf stomatal conductance was more sensitive to ECiw than the net photosynthesis rate, leading to higher intrinsic water use efficiency (WUE) in higher ECiw, whereas the LF did not affect the intrinsic WUE. Carbon isotope discrimination was inhibited by ECiw, but was not affected by LF. ECiw reduced the carboxylation efficiency, photosynthetic capacity, photorespiration rate, apparent quantum yield of CO2 and irradiance-saturated rate of gross photosynthesis; however, LF did not influence any of these responses. Total C and N accumulation in plants leaves was markedly increased with either decreasing ECiw or increasing LF. CONCLUSIONS: The present study shows that higher ECiw depressed leaf gas exchange, photosynthesis capacity and total C and N accumulation in leaves, but enhanced intrinsic WUE. Somewhat surprisingly, higher LF did not affect the intrinsic WUE but enhanced the total C and N accumulation in leaves.

Effects of Rainfall Exclusion Treatment on Photosynthetic Characteristics of Black Locust in the Sub-Humid Region of the Loess Plateau, China.

The mesic-origin species Robinia pseudoacacia L. (black locust) is widely planted in the semiarid and sub-humid areas of the Loess Plateau for the reforestation of vegetation-degraded land. Under the scenario of changing precipitation patterns, exploring the response of photosynthesis to drought allows us to assess the risk to sustainable development of these plantations. In this study, paired plots were established including the control and a treatment of 30% exclusion of throughfall (since 2018). The photosynthetic characteristics were investigated using a portable photosynthesis system for four periods in the full-leaf growing season of 2021-2022, the fourth and fifth years, on both treated and controlled sampling trees. Leaf gas exchange parameters derived from diurnal changing patterns, light response curves, and CO2 response curves showed significant differences except for period II (9-11 September 2021) between the two plots. The photosynthetic midday depression was observed in 2022 in the treated plot. Meanwhile, the decline of net photosynthetic rate in the treated plot was converted from stomatal limitation to non-stomatal limitation. Furthermore, we observed that black locust adapted to long-term water deficiency by reducing stomatal conductance, increasing water use efficiency and intrinsic water use efficiency. The results demonstrate that reduction in precipitation would cause photosynthesis decrease, weaken the response sensitivity to light and CO2, and potentially impair photosynthetic resilience of the plantations. They also provide insights into the changes in photosynthetic functions under global climate change and a reference for management of plantations.

Effects of 5-HT on the cold resistance of mangrove Kandelia obovata seedlings.

5-hydroxytryptamine (5-HT) participates in plant growth and development, and can also delay senescence and cope with abiotic stress. To explore the role of 5-HT in regulating the abilities of mangrove in cold resis-tance, we examined the effects of cold acclimation and the spraying of p-chlorophenylalanine (p-CPA, 5-HT synthesis inhibitor) on leaf gas exchange parameters and CO2 response curves (A/Ca), as well as the endogenous phytohormone content levels in the mangrove species Kandelia obovata seedlings under low temperature stress. The results showed that low temperature stress significantly reduced the contents of 5-HT, chlorophyll, endogenous auxin (IAA), gibberellin (GA), and abscisic acid (ABA). It weakened the CO2 utilization abilities of plants and reduced net photosynthetic rate, which ultimately reduced carboxylation efficiency (CE). Under low temperature stress, exogenous p-CPA reduced the contents of photosynthetic pigments, endogenous hormones, and 5-HT in the leaves, which aggravated the damages caused by low temperature stress on photosynthesis. By enhancing cold acclimation abilities, the endogenous IAA content in the leaves could was reduced under low temperature stress, promoted the production of 5-HT, improved the contents of photosynthetic pigments, GA, and ABA, as well as enhanced photosynthetic carbon assimilation abilities, which would increase photosynthesis in the K. obovata seedlings. Under cold acclimation conditions, the spraying of p-CPA could significantly inhibit the synthesis of 5-HT, promote the production of IAA, and reduce the contents of photosynthetic pigments, GA, ABA, and CE, which would weaken the effects of cold acclimation by improving the cold resistance of mangroves. In conclusion, cold acclimation could improve the cold resistance abilities of K. obovata seedlings by regulating photosynthetic carbon assimilation capacity and the contents of endogenous phytohormone. 5-HT synthesis is one of the necessary conditions for improving the cold resistance abilities of mangroves.

Biomass allocation and gas exchange are affected by light conditions in endangered Cedrela salvadorensis (Meliaceae) seedlings / Asignación de biomasa e intercambio de gases son afectados por las condiciones de luz en plántulas de Cedrela salvadorensis (Meliaceae) en peligro de extinción

Abstract:The determination of favorable light habitat conditions per species and life stage is transcendental, for both ex situ and in situ conservation strategies of endangered forest tree species, and for their utilization as plantation trees. This becomes especially important when planting material is scarce. We studied the multivariate responses in biomass allocation and in gas exchange to light and to CO2 in Cedrela salvadorensis seedlings, grown under similar light conditions as those this species faces in nature. During a period of 135 days, groups of ten seedlings were put under 75, 45, 15 and 3.5 % of full sun exposure obtained with neutral shade cloth, under nursery conditions. A series of biomass allocation variables and detailed gas exchange parameters (photosynthesis response curves to light and to internal carbon concentration) were measured at the end of the growth period in plants of the four treatments. According to the principal component analyses, highest values of gas exchange response were associated with the lower values of biomass allocation traits. These changes can be associated with resource-conservative and resource-acquisitive strategies, where the C. salvadorensis seedlings acclimatize their traits for the exploration and exploitation of light, to high or to dim light environment, respectively. The multivariate analyses also showed that the plants had a high performance at 45 % of light environments. These results suggest that 45 % of light environment was the optimal light habitat of this species at the tested developing stage. Our results have important implications to choose the best natural habitat for a successful establishment of C. salvadorensis. We propose practical considerations for programs of reforestation or reintroduction where this species be involved. Rev. Biol. Trop. 64 (3): 1143-1154. Epub 2016 September 01.

ResumenLa determinación de las condiciones lumínicas favorables por especie y estado de vida es trascendental para las estrategias de conservación ex situ y in situ de especies de árboles en peligro de extinción, y su utilización como plantaciones forestales. Esto se vuelve especialmente importante cuando el material de siembra es escaso. Aquí, nosotros estudiamos las respuestas en asignación de biomasa y en intercambio de gases a luz y CO2 en plántulas de Cedrela salvadorensis crecidas bajo condiciones lumínicas similares a las que esta especie enfrenta en la naturaleza. Durante 135 días, grupos de diez plántulas fueron colocadas bajo condiciones de 75, 45, 15 y 3.5 % de exposición total al sol obtenidas por medio de sarán bajo condiciones de vivero. Una serie de variables de asignación de biomasa y parámetros de intercambio de gases (fotosíntesis según curvas de respuesta a la luz y a la concentración de carbono interno) fueron medidas al final del periodo de crecimiento en las plantas de los cuatro tratamientos. De acuerdo con los análisis de componentes principales, valores altos de respuesta de intercambio de gases están asociados con valores bajos de rasgos de asignación de biomasa. Los cambios observados se encuentran asociados con las estrategias recurso-conservativas y recurso-adquisitivas donde C. salvadorensis aclimata sus rasgos para la exploración y explotación de luz en ambientes con escasa o excesiva radiación lumínica, respectivamente. Los análisis multivariados muestran también que las plantas tienen un alto rendimiento a 45 % de luz ambiental. Estos resultados sugieren que el 45 % de ambiente lumínico es el hábitat lumínico óptimo de esta especie en el estado de desarrollo estudiado. Nuestros resultados tienen importantes implicaciones para escoger el mejor hábitat natural para un exitoso establecimiento de C. salvadorensis. Por esto, proponemos consideraciones prácticas para programas de reforestación y reintroducción donde esta especie estaría involucrada.